1. Field of the Invention
The present invention relates to an irregular pattern detector, which captures, as images, irregular patterns, such as fingerprints.
2. Description of the Prior Art
A fingerprint ID apparatus is known as one of means of identifying persons. The fingerprint ID apparatus is constituted substantially by a pattern detection part capturing an irregular pattern of a fingerprint as an image, and a processing part for processing the images captured by the pattern detection part. Improvements in irregular pattern detectors such as the fingerprint ID apparatus have resulted in improved performance of the fingerprint ID apparatus.
FIG. 1 is a partially sectioned view of constitution of a conventional irregular pattern detector disclosed in Japanese Patent Application Laid-open No. 6-83944. In this drawing, the conventional irregular pattern detector has a light guide body 102 made of transparent materials such as glass or acrylic resin. A plane 103 is touched by subjects 101 such as a finger, the finger having irregular patterns thereon. A plane 104 intersects the plane 103 at a suitable angle and receives an illuminating light L100 therein. A plane 105 reflects a reflection light L101, which is reflected by the irregular patterns of the subject 101 placed on the plane 103, and controls the reflection light L101 approximately parallel to the plane 103. An imaging lens 108 focuses the reflection light L101 onto a camera device 109. A reflection mirror 110 reflects light from the imaging lens 108 at an angle to guide the reflection light to the camera device 109.
The plane 104 is flush with the plane 105. Therefore, an angle xcex2 of the plane 104 or the plane 105 with respect to the plane 107 facing the plane 106 is set to 20xc2x0, for example. An interface between the subject 101 and the plane 103 is further irradiated with the reflection light L101 from outside of the plane 104. The reflection light L101 reflected by the irregular patterns of the subject 101 is further reflected by the plane 105, focused by the imaging lens 108, and reflected by the reflection mirror 110. Consequently, images of the irregular patterns of the subject 101 are taken by the camera device 109 such as a CCD, for example.
FIG. 2 is a partially sectioned view of a simplified optical system, which is similar to the conventional irregular pattern apparatus as shown in FIG. 1. In FIG. 2, as compared with FIG. 1, the plane 103 corresponds to a plane 111, the plane 105 corresponds to a mirror 112, the imaging lens 108 corresponds to a lens 113, and the camera device 109 corresponds to a plane 114. A plane 115 and the plane 111 are related with respect to the mirror 112 as mirror images. The plane 115 is not perpendicular to an optical axis of the lens 113, and accordingly variations in the distance from points A, B and C on the plane 115 to the lens 113 occur, and variations of optical magnification at points Axe2x80x2, Bxe2x80x2 and Cxe2x80x2 occur. FIGS. 3A and 3B are plan views of images, respectively, in the optical system as shown in FIG. 2. In FIG. 3A, a rectangular image of the subject 101 placed on the plane 111 is illustrated. In FIG. 3B, an image formed on the plane 114 is illustrated. As illustrated in FIG. 3A, when the image of the subject placed on the plane 111 has a rectangular shape, the image formed on the plane 114 has a trapezoidal shape owing to the lens 113 as illustrated in FIG. 3B.
When distance BBxe2x80x2 is reduced in order to scale down the irregular pattern detector, angles of line BBxe2x80x2 with respect to line AAxe2x80x2 or line BBxe2x80x2 are enlarged, respectively. In this case, the aforementioned deformation of the image is conspicuous.
As illustrated in FIG. 2, line DE crosses the optical axis of the lens 113 at a right angle, and line AC tilts toward the optical axis. Therefore, as illustrated in FIGS. 3A and 3B, the length in a direction of line AC is shortened as compared with the length in a direction of line DE. The ratio of a longitudinal direction to a lateral direction of the subject 101 placed on the plane 111 as a detection face is different from the ratio of a longitudinal direction to a lateral direction of the image formed on the plane 114 as a light-detecting face, and accordingly precise images are not obtained.
Accordingly, it is an object of the present invention to provide a compact irregular pattern detector, which obtains precise images without any deformation.
In order to achieve the object of the present invention, an irregular pattern detector comprises an irregular pattern detector, including a first optical system having a light source; a transparent light guide body having an incident face receiving incident light from the light source of the first optical system, a detection face provided to face the incident face and for placing a subject thereon, a curved surface reflecting scattering light from the detection face, an optical absorbing face provided to face the curved surface and having an opening part outputting the reflection light from the curved surface; and a second optical system for guiding the light from the opening part of the optical absorbing face of the transparent light guide body to a camera device.
Here, the transparent light guide body may be provided on the first optical system.
The scattering light may be directly reflected with the curved surface to guide through the opening part to outside.
The curved surface of the transparent light guide body may be a spherical mirror, and a spherical radius of the spherical mirror may be twice as long as distance between a central point of the spherical mirror and an intersection point intersecting the spherical radius passing the central point of the spherical mirror with a perpendicular extending from a center of the opening part to the spherical radius.
The spherical mirror may form a telecentric system at a side of the subject, and the second optical system may form a telecentric system at an imaging side.
The curved surface of the transparent light guide body may be a spherical mirror, and a spherical radius of the spherical mirror may be within the range of 1.7 to 1.9 times as long as distance between a central point of the spherical mirror and an intersection point intersecting the spherical radius passing the central point of the spherical mirror with a perpendicular extending from a center of the opening part to the spherical radius.
The second optical system may correct longitudinal and lateral magnification of the light from the opening part to guide the corrected light to the camera device.
The detection face of the transparent light guide body may be a cylindrical shaped side face.
The second optical system may bend the light from the opening part to guide the light to the camera device.
The light source of the first optical system may be a light-emitting diode array provided on a substrate, and the camera device may be provided on the substrate.
The light source of the first optical system may be a light-emitting diode array provided on a substrate, and the incident face of the transparent light guide body may be constituted by a plurality of curved surfaces.